1. Field of the Invention
The invention relates to a process for the reduction of carboxylic acid halides to aldehydes and to a reagent for the reduction.
2. Description of the Prior Art
A widely used process for the catalytic reduction of carboxylic acid chlorides to the corresponding aldehydes is the Rosenmund reduction. In this process, carboxylic acid chlorides are hydrogenated using a suitable catalyst, usually 5% palladium on barium sulfate, poisoned with a mixture of quinoline and sulfur to prevent further reduction to the alcohol. This process has the economic disadvantage that pressure equipment is required. An additional disadvantage is that certain functional groups other than the acid chloride group are reduced: for example, nitro groups are reduced to amino groups.
Most hydride reducing agents reduce carboxylic acid chlorides to the corresponding alcohols. However, at very low temperatures, for example -80.degree. C. to -70.degree. C., lithium tri-t-butoxyaluminum hydride and sodium borohydride may be used to reduce acid chlorides to the corresponding aldehydes. Certain complex hydride reducing agents can be used for the reduction of specific acid chlorides to aldehydes; for example, sodium trimethoxyborohydride reduces most acid chlorides to the corresponding aldehydes. Certain complex hydride reducing agents can be used for the reduction of specific acid chlorides to aldehydes; for example, sodium trimethoxyborohydride reduces most acid chlorides to the corresponding alcohol, but reduces triacetylshikimic acid chloride to the corresponding aldehyde.